1. Field of the Invention
The present invention generally relates to a method of producing a pipe adapted to be attached to another pipe or hose. More particularly, the present invention relates to a method of producing a pipe that can suitably be applied to pipes, etc., having an O-ring for sealing.
2. Description of Related Art
A spinning method has conventionally been used for forming pipes adapted to have other pipes or hoses connected thereto. Such pipes are conventionally used to carry a high-pressure or low-pressure fluid. The attached pipes or pipe and hose include a cylindrical seal shape having a seal groove for holding an annularly recessed O-ring in the periphery thereof.
The spinning method is illustrated in FIGS. 20A and 20B. Pipe 9 is set on a spinning machine, and spinning roller 60 contacts a part of pipe 9 by pressing thereagainst where seal groove 16 is formed for holding an O-ring therein. Then, by rotating spinning roller 60 around the periphery of pipe 9 in the direction indicated by arrow a in FIG. 20B, while roller 60 spins or rotates in the direction indicated by arrow b in FIG. 20B, a part of outside diameter 61 of pipe 9 gradually has a recess formed therein, which is seal groove 16 for holding an O-ring.
However, the spinning method described above, which is the conventional method of forming a pipe with a cylindrical seal recess, has been found to certain problems. Namely, the material surface of the bottom face of seal groove 16 for holding an O-ring is pulled, and consequently, the material is drawn to the bottom face of the seal groove, as indicated by point R in FIG. 20B. As a result, in some cases, it is difficult to achieve the required roughness of the seal face, which in turn causes leaks due to defective sealing.
In addition, as the outside diameter of a pipe is pressed and then the seal groove for holding an O-ring is spun, time is required to remove the pipe from the press and set it onto the roller. As a result, it becomes more difficult to achieve the required concentricity between the outside diameter and seal groove bottom face of the pipe.